Valve for Controlling Gas Exchange, Especially in Internal Combustion Engines

ABSTRACT

A valve for controlling gas exchange, especially in internal combustion engines, comprises, at a valve stem, a stem end and at the other end thereof a valve cone. The valve cone and/or the valve stem are configured as hollow metal elements in such a manner that the hollow elements are entirely or partially filled with a metal foam. The interfaces between the metal and the metal foam are interlinked on the molecular level.

The present application is a division of U.S. application Ser. No.11/831,964, filed Aug. 1, 2007, which is a continuation ofPCT/EP2006/000485, filed Jan. 20, 2006, which claims priority to DEApplication 102005005041.7, filed Feb. 3, 2005, the contents of each ofwhich are incorporated herein by reference.

This invention relates to a valve for control of gas exchange,especially in internal combustion engines. Such valves are preferablyused as lightweight valves, as described in German Offenlegungsschrift[Unexamined Application] DE 19804053. Therein the valve cone and valvesealing plug together form a cavity; for weight reasons, the wallthicknesses of these hollow parts are chosen such that they correspondto less than one third of the stem diameter. However, in order to assuresufficient strength, the valve sealing plug in the known lightweightvalve is braced against the valve stem inside a radially interiorregion, and the valve cone is fixed with its upper end to the outside ofthe stem. This known structural form successfully improves thedeformation stiffness of the valve head compared with valves in which ahollow valve stem is made in one piece with the valve cone. In orderthat all strength requirements can also be satisfied under ignitionconditions in the engine, it is necessary in the known lightweightvalves to use expensive hardenable materials having high temperaturestability.

In contrast, the object of the present invention is to providelightweight valves of the type mentioned hereinabove, which valves canbe manufactured from less expensive material and otherwise satisfy therequirements of high-speed machines, especially internal combustionengines. Because of the danger of high vibrational loads in suchhigh-speed engines, special value is placed on achieving good dampingcharacteristics and at the same time minimizing the wall thickness inorder to save weight.

This object is achieved by a valve of the type mentioned hereinabove,comprising a valve cone at one end of a valve stem, the valve stemand/or valve cone being formed as hollow metal parts having a cavityfilled at least partly with metal foam to form a metal-foam body,wherein the metal-foam body formed in the valve cavity is bondedmetallically at the molecular level at the interfaces with the hollowmetal parts forming the valve. By the fact that the valve-forming hollowparts are completely or partly filled with metal foam, a high stiffeningeffect is achieved, thus making it possible to operate with thin wallthicknesses of the hollow parts forming the valve. To achieve both highstrength values and good damping characteristics, it is of substantialimportance that the hollow parts forming the valve are bondedmetallically at the molecular level over their entire surface with themetal foam.

Options for the metal foam include embodiments both with closed and withopen pores. Whereas the closed-pore metal foam offers higher strength,for example when the individual cells have substantially sphericalshape, a particular advantage of the open-pore embodiment is thatfilling with coolant, for example based on sodium, is possible.

In an expedient embodiment, the metal foam has a metal matrix comprisingbetween 5 and 20 vol %, preferably between approximately 8 and 10 vol %.Suitable materials for this purpose are Al, Zn and Fe foams or the like,a metal matrix based on AlSi7 being preferred.

In order to satisfy the requirements of low valve weight, an averagedensity of approximately 0.5 g/cm³ is desirable for the metal foam. Inthe case of an AlSi7 foam, this would correspond to values ofapproximately 50 GPa for the modulus of elasticity and 185 MPa for thetensile strength.

As suitable starting material for the metal foam there can be chosen apowder mixture such that a blowing agent will generate a foam volume ofapproximately five times that of the starting material under the effectof heat.

Advantageously the entire hollow body comprising valve stem and valvehead is filled with metal foam. According to an advantageous method forthis purpose, it is provided that the starting material for the metalfoam is introduced through one open end of the valve stem in such a waythat the metal foam completely fills the valve cavity under the effectof heat, and its quantity is adjusted to swell beyond the filling end,after which the excess quantity of metal foam is removed and the fillingopening is sealed by welding.

Thus the swelling direction for propagation of the metal foam can bechosen as desired, for example via an opening at the stem end of thevalve stem in the direction of the valve head, or by filling theswelling powder through an opening of the valve bottom, for example withthe valve sealing plug removed, so that the powder flows toward theclosed stem end. After the filling operation, the powder is foamed underthe effect of heat, until it swells beyond the existing filling openingin the manner of the method suggested in the foregoing. The temperatureis to be selected such that the metal foam becomes permanently bonded tothe inside face of the hollow body of the valve.

In order to be able to economize on expensive material, the inventionfurther proposes that the metal envelope forming the valve be weldedtogether from a plurality of portions, which can be made of like orunlike materials.

In an advantageous embodiment, the valve head comprises a valve conemade in one piece with the valve stem as well as a valve sealing plug,joined to one another by electric welding. In this case it can beadvantageous for the valve stem to comprise a portion of Nimonic80A atthe head end of the valve as well as an end portion of hardenablematerial surrounding the stem end of the valve, the two portions beingjoined to one another by friction welding. The end portion, which is tobe kept as short as possible, is usually made of X45CrSi93 (DIN 1.4718).

FIG. 1 is a longitudinal section through a valve of one embodiment ofthe present invention.

A practical example of the invention is explained hereinafter on thebasis of FIG. 1. FIG. 1 shows a longitudinal section through a valvecomprising a hollow valve stem 1, a valve cone 2 formed thereon, a valvesealing plug 3 joined to valve cone 2 on the outer circumference bymeans of a weld 7 made by electric welding, as well as a stem end 4 atthe other end of valve stem 1. It is evident that solid stem end 4 isjoined by means of a weld 5 to hollow valve stem 1, for which purposethere is used a friction weld. The entire valve cavity is filled with ametal-foam body 6, and the metal foam at its interfaces with the hollowbody of the valve forms a molecular bond in the manner of a monolithicstructure.

1. A method for manufacturing a valve for control of gas exchange,suitable for internal combustion engines, the valve comprising a valvecone at one end of a valve stem, the valve stem and/or valve cone beingformed as hollow metal parts having a cavity filled at least partly withmetal foam to form a metal-foam body, wherein the metal-foam body formedin the valve cavity is bonded metallically at the molecular level at theinterfaces with the hollow metal parts forming the valve without the useof an interfacial layer of bonding material between the metal-foam bodyand the valve cavity, the method comprising: introducing startingmaterial for the metal foam through one open end of the valve stem insuch a way that the metal foam completely fills the valve cavity andmolecularly bonds with the valve, without the use of an interfaciallayer of bonding material between the metal foam and the valve cavity,under the effect of heat, and its quantity is adjusted to swell beyondthe filling end; removing the excess quantity of metal foam; and sealingthe filling opening.
 2. The method according to claim 1, furthercomprising processing the metal foam in such a way that the metal foamhas closed or open pores.
 3. The method according to claim 2, whereinthe metal foam has open pores, further comprising filling the open poreswith a coolant.
 4. The method according to claim 1, further comprisingforming the metal foam such that the metal foam has a metal matrixcomprising between 5 and 20 percent of the volume of the metal foam. 5.The method according to claim 4, further comprising forming the metalfoam such that the metal foam has a metal matrix comprising between 8and 10 percent of the volume of the metal foam.
 6. The method accordingto claim 1, further comprising forming the metal foam by a metal matrixbased on AlSi7.
 7. The method according to claim 6, further comprisingforming the metal foam such that the average density of the metal foamis approximately 0.5 g/cm³.
 8. The method according to claim 6, furthercomprising choosing a powder mixture as starting material for the metalfoam such that a blowing agent will generate a foam volume ofapproximately five times that of the starting material under the effectof heat.
 9. The method according to claim 1, further comprisingcompletely filling the valve stem and the valve cone with metal foam.10. The method according to claim 1, further comprising forming a metalenvelope forming the valve by welding together a plurality of portions,which are made of like or unlike materials.
 11. The method according toclaim 10, further comprising forming a valve head by joining the valvecone made in one piece with the valve stem as well as a valve sealingplug.
 12. The method according to claim 10, further comprising formingthe valve stem by joining by friction welding a portion of Nimonic80A atthe head end of the valve as well as an end portion of hardenablematerial surrounding the stem end of the valve.
 13. The method accordingto claim 12, further comprising making the end portion with X45CrSi93(DIN 1.4718).
 14. A method for manufacturing a valve for control of gasexchange, suitable for internal combustion engines, the valve comprisinga valve cone at one end of a valve stem, the valve stem and/or valvecone being formed as hollow metal parts having a cavity filled at leastpartly with metal foam to form a metal-foam body, wherein the metal-foambody formed in the valve cavity is bonded metallically at the molecularlevel at the interfaces with the hollow metal parts forming the valvewith the metal-foam body bonding directly to the metal parts forming thevalve, the method comprising: introducing starting material for themetal foam through one open end of the valve stem in such a way that themetal foam completely fills the valve cavity and molecularly bondsdirectly with the valve under the effect of heat, and its quantity isadjusted to swell beyond the filling end; removing the excess quantityof metal foam; and sealing the filling opening.
 15. The method accordingto claim 14, further comprising processing the metal foam in such a waythat the metal foam has open pores, and further comprising filling theopen pores with a coolant.
 16. The method according to claim 14, furthercomprising forming the metal foam such that the metal foam has a metalmatrix comprising between 5 and 20 percent of the volume of the metalfoam.
 17. The method according to claim 16, further comprising formingthe metal foam such that the metal foam has a metal matrix comprisingbetween 8 and 10 percent of the volume of the metal foam.
 18. The methodaccording to claim 14, further comprising forming the metal foam suchthat the average density of the metal foam is approximately 0.5 g/cm3.19. The method according to claim 14, further comprising forming themetal foam by a metal matrix based on AlSi7.
 20. The method according toclaim 14, further comprising choosing a powder mixture as startingmaterial for the metal foam such that a blowing agent will generate afoam volume of approximately five times that of the starting materialunder the effect of heat.